1. Field of the Invention
The invention generally relates to a system and method for supplying power to a vehicle.
2. Background Art
Hybrid electric vehicles and fuel cell vehicles may use an electrical energy storage system to provide electrical energy to the vehicle and to capture electrical energy generated by the vehicle such as during a braking event.
A high voltage battery system is an example of one such electrical energy storage system. A high voltage battery system can include a number of series connected energy storage units, or modules. Each module may contain one or more series connected energy storage cells, or batteries.
Because of the battery and module series connections, the performance of a high voltage battery system is generally limited by the performance of the battery with the lowest voltage. As a result, the batteries used in a high voltage battery system are generally selected such that their voltages are approximately equal, e.g., within a few milli-volts of each other. Such selection allows the high voltage battery system to operate without being limited by a lowest-voltage battery.
Once a high voltage battery system has been exposed to various current levels and temperature conditions, the battery voltages may deviate from each other. This voltage deviation may impact the performance of the high voltage battery system and thus impact overall vehicle performance and fuel economy.
Temperature deviations between batteries may also affect high voltage battery system performance and thus vehicle performance. Some high voltage battery system designs attempt to minimize temperature differences by locating the modules within close proximity of each other in order to facilitate thermal management. This strategy, however, may limit design and packaging options.
If a battery of a high voltage battery system becomes inoperable, the vehicle may be disabled or its performance may be significantly reduced until a replacement battery is installed.
Reconditioning of a high voltage battery system generally requires that the entire system be charged up to, for example, approximately 100% state of charge, discharged to approximately 10% state of charge, and then recharged back to approximately 50% state of charge. This procedure removes most battery memory effects and reduces voltage and state of charge deviations between batteries. Because of the battery and module series connections, the effectiveness of this reconditioning procedure is limited by, during discharge, the weakest battery, i.e., the battery with the lowest state of charge, and limited by, during charge, the strongest battery, i.e., the battery with the highest state of charge. Reconditioning of a high voltage battery system cannot be performed while the vehicle is in operation. Reconditioning of a high voltage battery system typically takes place at a vehicle service center.
A power supply system is desired that can operate with energy storage units of varying voltages and temperatures, that can correct voltage and temperature deviations, and that can continue to provide power when an energy storage unit is inoperable. A power supply system is also desired that can recondition an energy storage unit during vehicle operation.
Background information may be found in U.S. Pat. Nos. 5,710,504; 5,931,245; 6,281,662 B1; and 6,801,014 B1. Background information may be found in U.S. Patent Application Publication Numbers: 2005/0029987 A1 and 2005/0077875 A1.